This invention relates to the gravity blending of particulate material such as small plastic pellets, etc.
The purpose of such gravity blending is to extract samples of particulate material from different locations within a bin and re-mix the thus extracted portions of particulate material to provide a more uniform blend of particulate material for subsequent manufacturing operations. Such blending tends to improve the uniformity of the ultimate plastic product or products resulting from manufacturing operation.
The invention relates in particular to gravity blending of the type set forth in U.S. Pat. No. 3,268,215 to Burton (Aug. 23, 1966) assigned to Allied Industries, Inc. of Houston, Tex.
The Burton-type of gravity blending operations involves the discharge of particulate material from a main bin (usually cylindrical with a conical base) by way of a series of generally upright or vertically extending conduits, commonly termed "down comers". Such down comers are provided with a plurality of openings along their longitudinal length, with various varied spacing patterns of such openings usually being provided with various of these down comers.
In the practice of the Burton invention, the dynamics of the particulate material discharge operation, influenced by the presence of particulate material in the bin and the generally fluidized nature of such particulate material as caused by pneumatic conveying of particulate material to the upper portion of the bin during bin filling, tends to cause particulate material to be discharged from any particular down comer at any time generally or mainly from only the upper most open down comer opening located first above the top of the mass of particulate material within the bin. This phenomena is commonly referred to as the "top hole" gravity blending method.
The particulate material thus discharged from the bin, is conveyed by the down-comers to a collecting chamber located beneath the bin where the variously extracted samples or segments of particulate material from different bin locations are integrated or comingled in a collecting chamber. The comingled particulate material within the collecting chamber is then conveyed downwardly through conventional means such as rotary air locks, possibly augmented by a subsequent slide or control valve to a pneumatic conveying line. Blended particulate material reaching the pneumatic conveying line may be transmitted directly to storage or user facilities or may be recirculated through the gravity blender apparatus to provide still further and/or enhanced blending.
In the practice of such gravity blending operations, control over or reduction of fines in particulate material being handled by the gravity blender apparatus may be obtained by employing collecting chamber venting arrangements. One such advantageous blending chamber venting arrangement is featured in U.S. Pat. No. 3,936,037 to Leonard, Jr. (Feb. 3, 1976) also assigned to Allied Industries, Inc.
The present invention is directed to apparatus and methods intended to improve the operations of prior art such as that noted above and will now be considered.